This invention relates to a circuit arrangement for igniting and operating an electrodeless discharge lamp provided with a bridge commutator having two switching elements each having an emitter electrode (source) and a control electrode (gate) and a parasitic capacitance in between, said switching elements being alternately switched to a conducting state by means of a resonant control circuit which is coupled to an oscillator via a transformer.
A circuit arrangement of the type described in the opening paragraph is known from U.S. Pat. No 5,200,672. The known lamp is suitable for operating a low-pressure mercury discharge lamp. In the known circuit arrangement, the lamp is operated by means of a frequency of 13.56 MHz. Such a high operating frequency requires the use of a crystal oscillator for realizing a sufficiently stable frequency. An electrodeless discharge lamp which is frequently used in practice is operated at an operating frequency between 1 and 3 MHz, which imposes less stringent requirements on the stability of the operating frequency. In the known circuit arrangement, each control electrode is directly connected to a relevant secondary winding of the transformer.
A drawback of the known circuit arrangement is that pulsatory currents during the periods when each switching element is switched to a conducting state lead to distortion of the output voltage of the transformer.